The dynamic control of thermal transport properties in solids must contend with the fact that phonons are inherently broadband. Thus, efforts to create reversible thermal conductivity switches have resulted in only modest on/off ratios, since only a relatively narrow portion of the phononic spectrum is impacted. Here, we report on the ability to modulate the thermal conductivity of topologically networked materials by nearly a factor of four following hydration, through manipulation of the displacement amplitude of atomic vibrations. By varying the network topology, or crosslinked structure, of squid ring teeth-based bio-polymers through tandem-repetition of DNA sequences, we show that this thermal switching ratio can be directly programmed. This on/off ratio in thermal conductivity switching is over a factor of three larger than the current state-of-the-art thermal switch, offering the possibility of engineering thermally conductive biological materials with dynamic responsivity to heat.

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In this work, the effect of laser fluence on Au nanoparticles synthesized via laser ablation in liquids is studied for 1064 nm irradiation with 25 ps pulses. Particle size and polydispersity is found to display a negative trend with fluences up to ∼14 J cm(-2). Erratic size tendencies are observed at low fluences, i.e. slightly above the ablation threshold. This overall behavior is reconciled with recent computational studies and to fluctuations in ablation due to surface morphology. The effectiveness of the commonly used surfactant sodium dodecyl sulfate (SDS) is shown to diminish at higher fluence due to pyrolysis. In addition, shadowgraph imaging of the cavitation bubble is shown as a useful technique for determining the ablation threshold. Our findings are in good agreement with threshold values determined by traditional methods and are comparable to computational values, when differences in pulse duration are taken into account.

As evidenced by the growth of additive manufacturing, there is extensive value in customization, both in terms of chemistry and structure. Direct laser writing is a promising approach to the maskless patterning of a broad range of nano to microscale materials. We employ a methodology using laser-induced solvothermal voxels, which combines the control of solvothermal chemistry for nanoparticle synthesis with the patterning abilities of direct laser writing, enabling the integration of nanocrystalline oxides, metals, and mixed metal oxides and alloys. We present an expanded range of materials that can be easily fabricated through this method and explore how this process can be used for 2.5D topographical patterning and layering with potential applications for catalysis and sensing.

been made by introducing disorder in the systems via alloying, complex crystal-engineering, [4,5] and by creating interfaces in thin films. [2] Hicks and Dresselhaus originally proposed that quantum well structures should be capable of lowering the thermal conductivity with only a minor impact on the electrical conductivity; [6] note that the latter point is particularly important for the application in thermoelectrics. Experimentally the phenomenon has been demonstrated, e.g., by Hicks et al. [7] in the PbTe/(Pb,Eu)Te system and by Ohta et al. [8] in the SrTiO 3 /Sr(Ti,Nb)O 3 system. Layered structures that show reduced thermal conductivity have been reported for a number of other material systems as well, such as CaTiO 3 /SrTiO 3 , [9] W/ Al 2 O 3 , [10] PbTe/PbSe, [11] IrSb 3 /CoSb 3 , [12] AlN/GaN, [13] TiNiSn/ HfNiSn, [14] Si/Ge (including alloy variants), [15][16][17][18][19] GaAs/AlAs (including alloy variants), [20][21][22][23] Bi 2 Te 3 /Sb 2 Te 3 , [24] InAs/AlSb, [25] InGaAs/InGaAsP, [26] and Ge 2 Te 3 /Sb 2 Te 3 , [27] to name a few. Most such inorganic-inorganic interfaces utilize isoelectronic substitution to retain the electrical conductivity and the high degree of crystallinity of the samples, which essentially grow epitaxially. An exception are the crystalline-amorphous interfaces as reported, e.g., in the Al 2 O 3 /TiO 2 [28] and Si [29] systems. With regard to high-quality interfaces, inorganic-organic superlattices offer an attractive option to reduce thermal conductivity compared to a homogeneous inorganic thin film. Owing to the large acoustic impedances between the inorganic and organic materials, we may anticipate considerably lowered thermal boundary conductance across the inorganic-organic interface. [30] Remarkable results have been reported for, e.g., TiS 2 with organic molecules intercalated either electrochemically [31] or chemically [32] from an organic solution. We have, on the other hand, fabricated ZnO/benzene [33,34] and TiO 2 /benzene [35,36] superlattices using the gas-phase atomic/molecular layer deposition (ALD/MLD) thin-film technique to demonstrate reductions in thermal conductivity of several orders of magnitude. Among the benefits of the ALD/MLD technique over solution-based intercalation routes is that it allows the precise control of the introduction frequency of the organic layers within the inorganic matrix.The uniting concept to lower the thermal conductivity of superlattice and nanolaminate structures is to suppress phonon Nanoscale superlattice structures are known to significantly suppress the thermal conductivity in thin films due to phonon scattering at the interfaces of the mutually different layers. Here it is demonstrated that in addition to the number of interfaces, their spacing within the film can lead to a reduction in thermal conductivity. The proof-of-concept data are for ZnO/benzene thin films fabricated through sequential gas-surface reactions in atomic/ molecular layer precision using the atomic/molecular layer deposition technique. In comparison to...

Aluminum nitride (AlN) has garnered much attention due to its intrinsically high thermal conductivity. However, engineering thin films of AlN with these high thermal conductivities can be challenging due to vacancies and defects that can form during the synthesis. In this work, we report on the cross-plane thermal conductivity of ultra-high-purity single-crystal AlN films with different thicknesses (∼3–22 μm) via time-domain thermoreflectance (TDTR) and steady-state thermoreflectance (SSTR) from 80 to 500 K. At room temperature, we report a thermal conductivity of ∼320 ± 42 W m–1 K–1, surpassing the values of prior measurements on AlN thin films and one of the highest cross-plane thermal conductivities of any material for films with equivalent thicknesses, surpassed only by diamond. By conducting first-principles calculations, we show that the thermal conductivity measurements on our thin films in the 250–500 K temperature range agree well with the predicted values for the bulk thermal conductivity of pure single-crystal AlN. Thus, our results demonstrate the viability of high-quality AlN films as promising candidates for the high-thermal-conductivity layers in high-power microelectronic devices. Our results also provide insight into the intrinsic thermal conductivity of thin films and the nature of phonon-boundary scattering in single-crystal epitaxially grown AlN thin films. The measured thermal conductivities in high-quality AlN thin films are found to be constant and similar to bulk AlN, regardless of the thermal penetration depth, film thickness, or laser spot size, even when these characteristic length scales are less than the mean free paths of a considerable portion of thermal phonons. Collectively, our data suggest that the intrinsic thermal conductivity of thin films with thicknesses less than the thermal phonon mean free paths is the same as bulk so long as the thermal conductivity of the film is sampled independent of the film/substrate interface.

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